Click the PGN recorder link when posting. In the popup window, all you have to do is "click and click" and the piece will move. To erase a move, click "<" button and re-enter the move. You can play through the game before sending it to your post. After you have finished, just click "Send PGN Now" and the PGN will be wrapped in pgn tags and be sent to your post. After the PGN has been sent to your post, you are free to add {comments} or (variations).